Control of In-MOF topologies and tuning of porosity through ligand structure, functionality and interpenetration: Selective cationic dye exchange

Tuning of porosity in MOFs is best accomplished through isoreticular synthesis by employing organic linkers of varying dimensions and chemical functionalities, but with similar connectivity dispositions. In this scenario, the connectivity attributes of both linker and metal ion SBUs are uniformly conserved. Leveraging the preponderant occurrence of 4-connecting [In(OCOR)4]¯ SBU of In(III) ion in the MOFs constructed from tetracarboxylate linkers in particular, we have investigated tuning of porosity by a subtle variation of the structures of organic linkers that lie within two extremes of tetrahedral and square planar connectivity dispositions. It is shown that solvothermal reactions of eight rationally-designed 4-connecting tetracarboxylate linkers featuring concave shapes with In(III) salt lead to anionic In-MOFs of four different topologies, i.e., dia, neb, lon and pts. All the In-MOFs exhibit considerable sorption of gases with varying capacities, determined by the porosities that are tuned by structure, functionality and magnitude of interpenetration. The applicability of In-MOFs with tunable porosity is demonstrated for highly selective dye exchange in that only methylene blue is captured selectively from amongst nine cationic, neutral and anionic dyes. Thus, a direct correspondence between subtle changes in the structural attributes of 4-connecting linkers and MOF topologies is shown to enable a blueprint for synthesis of In-MOFs of tunable porosities that permit ion exchange-based selective dye adsorption.